feat: implement L1-L7 context tree for multi-layered memory management

Implements Pillar 2 (Multi-layered Context Management) with a 7-tier
hierarchical memory system from real-time market data to generational
trading wisdom.

## New Modules
- `src/context/layer.py`: ContextLayer enum and metadata config
- `src/context/store.py`: ContextStore for CRUD operations
- `src/context/aggregator.py`: Bottom-up aggregation (L7→L6→...→L1)

## Database Changes
- Added `contexts` table for hierarchical data storage
- Added `context_metadata` table for layer configuration
- Indexed by layer, timeframe, and updated_at for fast queries

## Context Layers
- L1 (Legacy): Cumulative wisdom (kept forever)
- L2 (Annual): Yearly metrics (10 years retention)
- L3 (Quarterly): Strategy pivots (3 years)
- L4 (Monthly): Portfolio rebalancing (2 years)
- L5 (Weekly): Stock selection (1 year)
- L6 (Daily): Trade logs (90 days)
- L7 (Real-time): Live market data (7 days)

## Tests
- 18 new tests in `tests/test_context.py`
- 100% coverage on context modules
- All 72 tests passing (54 existing + 18 new)

## Documentation
- Added `docs/context-tree.md` with comprehensive guide
- Updated `CLAUDE.md` architecture section
- Includes usage examples and best practices

Closes #15

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/context/store.py

@@ -0,0 +1,193 @@
+"""Context storage and retrieval for the 7-tier memory system."""
+
+from __future__ import annotations
+
+import json
+import sqlite3
+from datetime import UTC, datetime
+from typing import Any
+
+from src.context.layer import LAYER_CONFIG, ContextLayer
+
+
+class ContextStore:
+    """Manages context data across the 7-tier hierarchy."""
+
+    def __init__(self, conn: sqlite3.Connection) -> None:
+        """Initialize the context store with a database connection."""
+        self.conn = conn
+        self._init_metadata()
+
+    def _init_metadata(self) -> None:
+        """Initialize context_metadata table with layer configurations."""
+        for config in LAYER_CONFIG.values():
+            self.conn.execute(
+                """
+                INSERT OR REPLACE INTO context_metadata
+                (layer, description, retention_days, aggregation_source)
+                VALUES (?, ?, ?, ?)
+                """,
+                (
+                    config.layer.value,
+                    config.description,
+                    config.retention_days,
+                    config.aggregation_source.value if config.aggregation_source else None,
+                ),
+            )
+        self.conn.commit()
+
+    def set_context(
+        self,
+        layer: ContextLayer,
+        timeframe: str,
+        key: str,
+        value: Any,
+    ) -> None:
+        """Set a context value for a given layer and timeframe.
+
+        Args:
+            layer: The context layer (L1-L7)
+            timeframe: Time identifier (e.g., "2026", "2026-Q1", "2026-01",
+                "2026-W05", "2026-02-04")
+            key: Context key (e.g., "sharpe_ratio", "win_rate", "lesson_learned")
+            value: Context value (will be JSON-serialized)
+        """
+        now = datetime.now(UTC).isoformat()
+        value_json = json.dumps(value)
+
+        self.conn.execute(
+            """
+            INSERT INTO contexts (layer, timeframe, key, value, created_at, updated_at)
+            VALUES (?, ?, ?, ?, ?, ?)
+            ON CONFLICT(layer, timeframe, key)
+            DO UPDATE SET value = excluded.value, updated_at = excluded.updated_at
+            """,
+            (layer.value, timeframe, key, value_json, now, now),
+        )
+        self.conn.commit()
+
+    def get_context(
+        self,
+        layer: ContextLayer,
+        timeframe: str,
+        key: str,
+    ) -> Any | None:
+        """Get a context value for a given layer and timeframe.
+
+        Args:
+            layer: The context layer (L1-L7)
+            timeframe: Time identifier
+            key: Context key
+
+        Returns:
+            The context value (deserialized from JSON), or None if not found
+        """
+        cursor = self.conn.execute(
+            """
+            SELECT value FROM contexts
+            WHERE layer = ? AND timeframe = ? AND key = ?
+            """,
+            (layer.value, timeframe, key),
+        )
+        row = cursor.fetchone()
+        if row:
+            return json.loads(row[0])
+        return None
+
+    def get_all_contexts(
+        self,
+        layer: ContextLayer,
+        timeframe: str | None = None,
+    ) -> dict[str, Any]:
+        """Get all context values for a given layer and optional timeframe.
+
+        Args:
+            layer: The context layer (L1-L7)
+            timeframe: Optional time identifier filter
+
+        Returns:
+            Dictionary of key-value pairs for the specified layer/timeframe
+        """
+        if timeframe:
+            cursor = self.conn.execute(
+                """
+                SELECT key, value FROM contexts
+                WHERE layer = ? AND timeframe = ?
+                ORDER BY key
+                """,
+                (layer.value, timeframe),
+            )
+        else:
+            cursor = self.conn.execute(
+                """
+                SELECT key, value FROM contexts
+                WHERE layer = ?
+                ORDER BY timeframe DESC, key
+                """,
+                (layer.value,),
+            )
+
+        return {row[0]: json.loads(row[1]) for row in cursor.fetchall()}
+
+    def get_latest_timeframe(self, layer: ContextLayer) -> str | None:
+        """Get the most recent timeframe for a given layer.
+
+        Args:
+            layer: The context layer (L1-L7)
+
+        Returns:
+            The latest timeframe string, or None if no data exists
+        """
+        cursor = self.conn.execute(
+            """
+            SELECT timeframe FROM contexts
+            WHERE layer = ?
+            ORDER BY updated_at DESC
+            LIMIT 1
+            """,
+            (layer.value,),
+        )
+        row = cursor.fetchone()
+        return row[0] if row else None
+
+    def delete_old_contexts(self, layer: ContextLayer, cutoff_date: str) -> int:
+        """Delete contexts older than the cutoff date for a given layer.
+
+        Args:
+            layer: The context layer (L1-L7)
+            cutoff_date: ISO format date string (contexts before this will be deleted)
+
+        Returns:
+            Number of rows deleted
+        """
+        cursor = self.conn.execute(
+            """
+            DELETE FROM contexts
+            WHERE layer = ? AND updated_at < ?
+            """,
+            (layer.value, cutoff_date),
+        )
+        self.conn.commit()
+        return cursor.rowcount
+
+    def cleanup_expired_contexts(self) -> dict[ContextLayer, int]:
+        """Delete expired contexts based on retention policies.
+
+        Returns:
+            Dictionary mapping layer to number of deleted rows
+        """
+        deleted_counts: dict[ContextLayer, int] = {}
+
+        for layer, config in LAYER_CONFIG.items():
+            if config.retention_days is None:
+                # Keep forever (e.g., L1_LEGACY)
+                deleted_counts[layer] = 0
+                continue
+
+            # Calculate cutoff date
+            from datetime import timedelta
+
+            cutoff = datetime.now(UTC) - timedelta(days=config.retention_days)
+            deleted_counts[layer] = self.delete_old_contexts(layer, cutoff.isoformat())
+
+        return deleted_counts